Field of the Disclosure
This disclosure relates to control components for turbochargers with Variable Turbine Geometry (VTG). More particularly, this disclosure relates to integrated vane-open stops that control the full open position of the VTG mechanism to regulate exhaust gas flow to the turbine.
Description of Related Art
Advantages of turbocharging include increased power output, lower fuel consumption and reduced pollutant emissions. The turbocharging of engines is no longer primarily seen from a high power performance perspective, but is rather viewed as a means of reducing fuel consumption and environmental pollution on account of lower carbon dioxide (CO2) emissions. Currently, a primary reason for turbocharging is using exhaust gas energy to reduce fuel consumption and emissions. In turbocharged engines, combustion air is pre-compressed before being supplied to the engine. The engine aspirates the same volume of air-fuel mixture as a naturally aspirated engine, but due to the higher pressure, thus higher density, more air and fuel mass is supplied into a combustion chamber. Consequently, more fuel can be burned, so that the engine's power output increases relative to the speed and swept volume.
In exhaust gas turbocharging, some of the exhaust gas energy, which would normally be wasted, is used to drive a turbine. The turbine includes a turbine wheel that is mounted on a shaft and is rotatably driven by exhaust gas flow. The turbocharger returns some of this normally wasted exhaust gas energy back into the engine, contributing to the engine's efficiency and saving fuel. A compressor, which is driven by the turbine, draws in filtered ambient air, compresses it, and then supplies it to the engine. The compressor includes a compressor wheel/impeller that is mounted on the same shaft so that rotation of the turbine wheel causes rotation of the compressor wheel/impeller.
This disclosure focuses on a Variable Turbine Geometry (VTG) aspect of turbochargers. VTG turbochargers utilize adjustable guide vanes that are pivotally connected to a lower ring and an upper vane ring, including various possible rings, and/or nozzle wall. These guide vanes are adjusted to control exhaust gas backpressure and turbocharger speed by modulating the exhaust gas flow to the turbine wheel. The guide vanes are pivoted by vane levers. Performance and flow to the turbine are influenced by changes of the flow angle to the turbine wheel by pivoting the guide vanes.
One goal of VTG turbochargers is to expand the usable flow rate range in practical applications while maintaining a high level of efficiency. To accomplish this, the turbine output is regulated by changing an inflow angle and inflow speed of the exhaust gas flow at a turbine wheel inlet. With VTG turbochargers, this is achieved using guide vanes in front of the turbine wheel that change their angle of attack with exhaust gas flow speed. This reduces lag at slow speeds while opening to prevent exhaust gas backpressure at higher speeds.
With VTG, turbocharger ratios can be altered as conditions change. When the guide vanes are in a closed position, the high circumferential components of the flow speed and a steep enthalpy gradient lead to a high turbine output and therefore to a high charging pressure. When the guide vanes are in a fully open position, the turbine reaches its maximum flow rate and the velocity vector of the flow has a large centripetal component. The advantage of this type of output control over bypass control is that the entire exhaust gas flow is always directed through the turbine and can be converted to output. Adjustments of the guide vanes can be controlled by various pneumatic or electrical regulators.
An exemplary exhaust-gas turbocharger shown in prior art FIGS. 1-3 from U.S. Pat. No. 7,886,536 includes a turbine housing and a bearing housing, with a rotating shaft. On one end the shaft carries the compressor wheel/impeller and on the shaft's other end the turbine wheel. Within the turbine housing on the side of the turbine wheel a volute is formed which in radial direction evolves into a throat. Inside the throat adjustable guide vanes are located.
The guide vanes are pivoted from a vane bearing ring and from a thrust- and bearing ring which is by a spacer kept at a certain distance from the vane bearing ring, and they are adjustable through an actuator that actuates the unison ring. A rotary motion of the unison ring with respect to the vane bearing ring is transmitted onto the guide vanes, which can be adjusted within a pre-determined range between the open position and the closed position.
Typically, the closed position of the guide vanes is used to establish the position of the vanes in relation to the actuator. Current vane learn methodology is to “learn” against the vane closed position. While the closed position of the guide vanes is relatively fixed, the actuator position that relates to the closed position of the guides vanes varies due to extensive stackup of clearances and component tolerances between the guide vanes and other components, such as the actuator. Due to fixed limited travel of the actuator, the open vane position will vary dependent on the learned vane closed position. The learned vane closed position results in the open vane position of the guide vanes in turbochargers varying from one turbocharger to another.
U.S. Pat. No. 7,886,536 discloses an “Exhaust-gas Turbocharger, Regulating Device for an Exhaust-gas Turbocharger and Vane Lever for a Regulating Device”. Vane levers with axial bosses have circularly curved contour segments that provide for rolling movement with the inner circumference of the unison ring. This allows the vane lever to roll against the unison ring, but does not stop against the unison ring at a full open position.
U.S. Pat. No. 8,328,520 discloses a VTG turbocharger with separately formed vane lever stops. The stop is embodied as a separate component that can be fixed in the guide grate for adjusting the minimum throughflow.
In certain applications, regulating the full open position can be key. Certain turbochargers require full flow capacity of the VTG that may have insufficient maximum flow capacity when the vanes do not fully open. It is desirable therefore to provide a method where the full vane open position is established by a fixed stop.